Patent document 1 (shown below) shows a combustion pressure sensor having a pressure detecting element mounted on an ignition plug, a fuel injection valve, or the like of an internal combustion engine, and an amplifying circuit (charge amplifier) which amplifies changes in the voltage of the pressure detecting element to output a pressure detection signal. In this combustion pressure sensor, the pressure detecting element is fixed on the outside of the combustion chamber with the fuel injection valve by a nut for fixing the fuel injection valve, and the amplifying circuit is provided at the sensor-fixing block at which the pressure detecting element is fixed.
Patent document 2 (shown below) shows an in-cylinder pressure detecting apparatus, in which a pressure detecting element is mounted on a tip-portion of the fuel injection valve for injecting fuel into the combustion chamber, and the in-cylinder pressure is detected using the pressure detecting element.